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Articles indexed Tuesday April 20 2010

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  • What is proper way to detect all available serial ports on Windows?

    - by Sorin Sbarnea
    There are several ways to list serial ports under Windows but I'm not sure what is the proper way: the way that does detect all serial ports that are available. One good code example is http://www.naughter.com/enumser.html - where there at 9 (nine!) ways of enumerating serial devices. The question is: what is the optimal way of doing it. Requirements: * to not open ports in order to check if they are available. * to be able to detect ports with different names than COMx.

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  • Runge-Kutta (RK4) integration for game physics

    - by Kai
    Gaffer on Games has a great article about using RK4 integration for better game physics. The implementation is straightforward but the math behind it confuses me. I understand derivatives and integrals on a conceptual level but I haven't manipulated equations in a long time. Here's the brunt of Gaffer's implementation: void integrate(State &state, float t, float dt) { Derivative a = evaluate(state, t, 0.0f, Derivative()); Derivative b = evaluate(state, t+dt*0.5f, dt*0.5f, a); Derivative c = evaluate(state, t+dt*0.5f, dt*0.5f, b); Derivative d = evaluate(state, t+dt, dt, c); const float dxdt = 1.0f/6.0f * (a.dx + 2.0f*(b.dx + c.dx) + d.dx); const float dvdt = 1.0f/6.0f * (a.dv + 2.0f*(b.dv + c.dv) + d.dv) state.x = state.x + dxdt * dt; state.v = state.v + dvdt * dt; } Can anybody explain in simple terms how RK4 works? Specifically, why are we averaging the derivatives at 0.0f, 0.5f, 0.5f, and 1.0f? How is averaging derivatives up to the 4th order different from doing a simple euler integration with a smaller timestep? After reading the accepted answer below, and several other articles, I have a grasp on how RK4 works. To answer my own questions: Can anybody explain in simple terms how RK4 works? RK4 takes advantage of the fact that we can get a much better approximation of a function if we use its higher-order derivatives rather than just the first or second derivative. That's why the Taylor series converges much faster than Euler approximations. (take a look at the animation on the right side of that page) Specifically, why are we averaging the derivatives at 0.0f, 0.5f, 0.5f, and 1.0f? The Runge-Kutta method is an approximation of a function that samples derivatives of several points within a timestep, unlike the Taylor series which only samples derivatives of a single point. After sampling these derivatives we need to know how to weigh each sample to get the closest approximation possible. An easy way to do this is to pick constants that coincide with the Taylor series, which is how the constants of a Runge-Kutta equation are determined. This article made it clearer for me: http://web.mit.edu/10.001/Web/Course%5FNotes/Differential%5FEquations%5FNotes/node5.html. Notice how (15) is the Taylor series expansion while (17) is the Runge-Kutta derivation. How is averaging derivatives up to the 4th order different from doing a simple euler integration with a smaller timestep? Mathematically it converges much faster than doing many Euler approximations. Of course, with enough Euler approximations we can gain equal accuracy to RK4, but the computational power needed doesn't justify using Euler.

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  • Several numpy arrays with SWIG

    - by Petter
    I am using SWIG to pass numpy arrays from Python to C++ code: %include "numpy.i" %init %{ import_array(); %} %apply (float* INPLACE_ARRAY1, int DIM1) {(float* data, int n)}; class Class { public: void test(float* data, int n) { //... } }; and in Python: c = Class() a = zeros(5) c.test(a) This works, but how can I pass multiple numpy arrays to the same function?

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  • mysql: can't set max_allowed_package to anything grater than 16MB

    - by sas
    I'm not sure if this is the right place to post these kind of questions, if it's not so, please (politely) let me know... :-) I need to save files greater than 16MB on a mysql database from a php site... I've already changed the c:\xampp\mysql\bin\my.cnf and set max_allowed_packet to 16 MB, and everything worked fine then I set it to 32 MB but there´s no way I can handle a file bigger than 16 MB I get the following error: 'MySQL server has gone away' (the same error I had when max_allowed_packet was set to 1MB) there must be some other setting that doesn´t allow me to handle files bigger than 16MB maybe the php client, I guess, but I don't know where to edit it this is the code I'm running when file.txt is smaller than 16.776.192 bytes long, it works fine, but if file.txt has 16.777.216 bytes i get the aforementioned error oh, and the field download.content is a longblob... $file = 'file.txt'; $file_handle = fopen( $file, 'r' ); $content = fread( $file_handle, filesize( $file ) ); fclose( $file_handle ); db_execute( 'truncate table download', true ); $sql = "insert into download( code, title, name, description, original_name, mime_type, size, content, user_insert_id, date_insert, user_update_id, date_update ) values ( 'new file', 'new file', 'sas.jpg', 'new file', '$file', 'mime', " . filesize( $file ) . ", '" . addslashes( $content ) . "', 0, " . db_char_to_sql( now_char(), 'datetime' ) . ", 0, " . db_char_to_sql( now_char(), 'datetime' ) . " )"; db_execute( $sql, true ); (the db_execute funcion just opens the connections and executes the sql stuff) running on windows XP sp2 server version: 5.0.67-community PHP Version 4.4.9 mysql client API version: 3.23.49 using: ApacheFriends XAMPP (Basispaket) version 1.6.8 that comes with + Apache 2.2.9 + MySQL 5.0.67 (Community Server) + PHP 5.2.6 + PHP 4.4.9 + PEAR + phpMyAdmin 2.11.9.2 ... this is part of the content of c:\xampp\mysql\bin\my.cnf # The MySQL server [mysqld] port= 3306 socket= "C:/xampp/mysql/mysql.sock" basedir="C:/xampp/mysql" tmpdir="C:/xampp/tmp" datadir="C:/xampp/mysql/data" skip-locking key_buffer = 16M # max_allowed_packet = 1M max_allowed_packet = 32M table_cache = 128 sort_buffer_size = 512K net_buffer_length = 8K read_buffer_size = 256K read_rnd_buffer_size = 512K myisam_sort_buffer_size = 8M

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  • How to use a servlet to repsond to a request for an object

    - by Rick
    I'm sure this is easy, but I don't work with website development very often and I'm lost on this one. I have a web application that needs to support multiple clients with different settings, icons and other content. The contents of these files are in separate directories for each client. What I would like to do is respond to a request sent to a jsp/java servlet. The servlet will look up the proper folder location in a database (I have the database stuff working) and send the actual object to the requesting page whether it is xml, graphic or video. How do I do that? What methods should I be using. Help I'm lost! :(

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  • Make HTML5 code look beautiful!

    - by blinry
    I'm looking for a command line program that pretty-prints (that is, indents, adds line breaks to, harmonizes the whitespace of) HTML5 code. It has to run under Linux (in case you're interested, I want to use it as an filter for nanoc). tidy does too much for me (heck, it alters my doctype!), vim too little. What do you use to make your HTML5 code look beautiful? Maybe there is a way to make tidy cooperate and not alter anything?

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  • Kubuntu: apt-get install of php5-dev: libtool version mismatch?

    - by pinkgothic
    (Warning, clueless-newbism ahead.) Background info: I'm actually trying to install/upgrade xdebug. sudo pecl install xdebug yields: downloading xdebug-2.0.5.tgz ... Starting to download xdebug-2.0.5.tgz (289,234 bytes) ............................................................done: 289,234 bytes 67 source files, building running: phpize sh: phpize: not found ERROR: `phpize' failed A quick google tells me that phpize is a part of a package called php5-dev, so off I ran to install that. My problem is that using sudo apt-get install php5-dev fails with this output: sudo apt-get install php5-dev Reading package lists... Done Building dependency tree Reading state information... Done Some packages could not be installed. This may mean that you have requested an impossible situation or if you are using the unstable distribution that some required packages have not yet been created or been moved out of Incoming. The following information may help to resolve the situation: The following packages have unmet dependencies: php5-dev: Conflicts: libtool (>= 2.2) but 2.2.6a-4 is to be installed E: Broken packages 2.2.6a-4 is greater than 2.2, so I'm not sure why it's hanging itself up at that point. I'm guessing the fact that it's not entirely numeric is throwing apt-get off? I can probably install xdebug manually (though I've never done this before, so picture me with a deer clueless-newb in headlights look here, violently shaking my head and begging for a simpler solution) rather than via pecl / aptitude, but is there a way I can make aptitude install php5-dev despite the bogus 'broken package' claim? Is it even bogus, or am I misreading the error message? Alternatively: Could I install phpize in some other way (e.g. via pear or pecl)?

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  • Why the composite component fails to parent controls?

    - by lyborko
    Hi, I created my own Component : TPage , which Contains Subcomponent TPaper (TPanel). The problem is, that when I put controls such as TMemo or TButton on the TPaper (which fills up nearly whole area), the controls do not load at all. see example below TPaper = class(TPanel) protected constructor Create(AOwner: TComponent);override; destructor Destroy;override; public procedure Paint; override; end; TPage = class(TCustomControl) private FPaper:TPaper; protected procedure CreateParams(var Params:TCreateParams); override; public constructor Create(AOwner: TComponent);override; destructor Destroy;override; published property Paper: TPaper read FPaper write FPaper; end; constructor TPage.Create(AOwner: TComponent); begin inherited Create(AOwner); PaperOrientation:=poPortrait; PaperSize:=psA4; PaperBrush:=TBrush.Create; PaperBrush.Color:=clWhite; PDFDocument:=Nil; FPaper:=TPaper.Create(Self); FPaper.Parent:=Self; FPaper.SetSubComponent(True); end; ... Memo1 is parented in TPaper (TPanel) at design-time, but after pressing "Run" it does not exist. procedure TForm1.btn1Click(Sender: TObject); begin if not Assigned(Memo1) then ShowMessage('I do not exist'); //Memo1 is nil end; Have you any idea what's wrong? Thanks a lot P.S Delphi 7 When I put TMemo inside TPaper and save the unit (Unit1), after inspection of associated dfm file, there is no trace of TMemo component. (Thats why it can not load to app.)

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  • Epoll in EPOLLET mode returning 2 EPOLLIN before reading from the socket

    - by Arkaitz Jimenez
    The epoll manpage says that a fd registered with EPOLLET(edge triggered) shouldn't notify twice EPOLLIN if no read has been done. So after an EPOLLIN you need to empty the buffer before epoll_wait being able to return a new EPOLLIN on new data. However I'm experiencing problems with this approach as I'm seeing duplicated EPOLLIN events for untouched fds. This is the strace output, 0x200 is EPOLLRDHUP that is not defined yet in my glibc headers but defined in the kernel. 30285 epoll_ctl(3, EPOLL_CTL_ADD, 9, {EPOLLIN|EPOLLPRI|EPOLLERR|EPOLLHUP|EPOLLET|0x2000, {u32=9, u64=9}}) = 0 30285 epoll_wait(3, {{EPOLLIN, {u32=9, u64=9}}}, 10, -1) = 1 30285 epoll_wait(3, {{EPOLLIN, {u32=9, u64=9}}}, 10, -1) = 1 30285 epoll_wait(3, <unfinished ...> 30349 epoll_ctl(3, EPOLL_CTL_DEL, 9, NULL) = 0 30306 recv(9, "7u\0\0\10\345\241\312\t\20\f\32\r\10\27\20\2\30\200\10 \31(C0\17\32\r\10\27\20\2\30"..., 20000, 0) = 20000 30349 epoll_ctl(3, EPOLL_CTL_DEL, 9, NULL) = -1 ENOENT (No such file or directory) 30305 recv(9, " \31(C0\17\32\r\10\27\20\2\30\200\10 \31(C0\17\32\r\10\27\20\2\30\200\10 \31("..., 20000, 0) = 10011 So, after adding fd number 9 I do receive 2 consecutive EPOLLIN events before having recving the file descriptor, the syscall trace shows how I do delete the fd before reading but it should only happen once, one per event. So either I am not reading the manpage properly or something is now working here.

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  • How does Asp.Net MVC compare to Java MVC frameworks

    - by sumek
    I've started my career as a Java developer, then moved to Asp.NET and recently to the Asp.Net MVC, which I like a lot. When developing in Java I used Struts1, which I remember as a hideous framework with loads of XML. Now I suspect that Java MVC frameworks have moved on from the Struts times. So how do modern Java MVC frameworks compare to the ASP.Net MVC? Which one of them is the most similar to the Asp.Net MVC?

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  • Extra arguments for Factory Girl

    - by J. Pablo Fernández
    I need to pass extra arguments to factory girl to be used in a callback. Something like this (but more complex really): Factory.define :blog do |blog| blog.name "Blah" blog.after_create do |blog| blog.posts += sample_posts blog.save! end end and then create it with something like this: Factory.create(:blog, :sample_posts => [post1, post2]) Any ideas how to do it?

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  • How to find the Biggest and smallest in Int[] Array using c#

    - by karthik
    If the array is as follows, int[] array = new int[] { 7, 4, 1, 8 }; I want to find the Biggest, smallest, second smallest, second biggest If the array is as follows, int[] array = new int[] { 7, 4, 1 }; I want to find the Biggest, smallest, second smallest If the array is as follows, int[] array = new int[] { 7, 4 }; I want to find the Biggest, smallest How can i achieve this programmaticly.

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  • How to sort output of "s3cmd ls"

    - by dba.in.ua
    Amazon "s3cmd ls" takes like this output: 2010-02-20 21:01 1458414588 s3://file.tgz.00 2010-02-20 21:10 1458414527 s3://file.tgz.01 2010-02-20 22:01 1458414588 s3://file.tgz.00 2010-02-20 23:10 1458414527 s3://file.tgz.01 2010-02-20 23:20 1458414588 s3://file.tgz.02 How to select all files of archive, ending at 0 ... X, with the latest date of fileset ? Bash, regexp ? Thanx!

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  • Selectedindex in listview, throwing up an error!

    - by Luke
    Hey guys, the following code shows what i am trying to do. private void btnEdit_Click(object sender, EventArgs e) { iDeliverySelected = lstDeliveryDetails.SelectedIndex; bool addEdit = false; } The selectedindex is throwing up the following error.. 'System.Windows.Forms.ListView' does not contain a definition for 'SelectedIndex' and no extension method 'SelectedIndex' accepting a first argument of type 'System.Windows.Forms.ListView' could be found (are you missing a using directive or an assembly reference?) Any ideas why? First time I have tried to use SelectedIndex, not sure if i am using it correctly?

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  • 2k rows update is very slow in MySQL

    - by sergeik
    Hi all, I have 2 tables: 1. news (450k rows) 2. news_tags (3m rows) There are some triggers on news table update which updating listings. This SQL executes too long... UPDATE news SET news_category = some_number WHERE news_id IN (SELECT news_id FROM news_tags WHERE tag_id = some_number); #about 3k rows How can I make it faster? Thanks in advance, S.

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  • when i run exe(MFC Dialog based application) in Win 2k3 it fails to run(MSJAVA.dll Missing error)

    - by Vikram
    when i run exe(MFC Dialog based application) in Win 2k3 Fails to run(MSJAVA.dll Missing error).but the same exe runs successfully in WIN xp Edit: As per the solution by Goz ,I have downloaded the MSJAVA.dll and tried to run the exe,but am getting the below error, "The Side-by-Side configuration information for "f:\test\TESTCSDATACHANGEEVENTS.EXE" contains errors. This application has failed to start because the application configuration is incorrect. Reinstalling the application may fix this problem (14001)."

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  • NSXMLDocument objectByApplyingXSLT with XSL Include

    - by Kristof
    I'm having some trouble with XSL-processing when there are stylesheets that include other stylesheets relatively. (the XML-files may be irrelevant but are included for completeness - code is at the bottom). Given the XML-file: <?xml version="1.0" ?> <famous-persons> <persons category="medicine"> <person> <firstname> Edward </firstname> <name> Jenner </name> </person> <person> <firstname> Gertrude </firstname> <name> Elion </name> </person> </persons> </famous-persons> and the XSL-file: <?xml version="1.0" ?> <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:xi="http://www.w3.org/2001/XInclude" version="1.0"> <xsl:template match="/"> <html><head><title>Sorting example</title></head><body> <xsl:apply-templates select="famous-persons/persons"> <xsl:sort select="@category" /> </xsl:apply-templates> </body></html> </xsl:template> <xsl:include href="included.xsl" /> </xsl:stylesheet> referencing this stylesheet in included.xsl: <?xml version="1.0"?> <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:xi="http://www.w3.org/2001/XInclude" version="1.0"> <xsl:template match="persons"> <h2><xsl:value-of select="@category" /></h2> <ul>Irrelevant</ul> </xsl:template> </xsl:stylesheet> how can I make it that the following code fragment: NSError *lError = nil; NSXMLDocument *lDocument = [ [ NSXMLDocument alloc ] initWithContentsOfURL: [ NSURL URLWithString: @"file:///pathto/data.xml" ] options: 0 error: &lError ]; NSXMLDocument *lResult = [ lDocument objectByApplyingXSLTAtURL: [ NSURL URLWithString: @"file:///pathto/style.xsl" ] arguments: nil error: nil ]; does not give me the error: I/O warning : failed to load external entity "included.xsl" compilation error: element include xsl:include : unable to load included.xsl I have been trying all sorts of options. Also loading XML documents with NSXMLDocumentXInclude beforehand does not seem to help. Is there any way to make the XSL processing so that a stylesheet can include another stylesheet in its local path?

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  • Have you actually convinced anybody to Scala?

    - by Lukasz Lew
    I had limited success myself. I was able to hype a few persons about Scala. But in fact none of them made a meaningful effort to try to switch (usually from Java). I would like to read both success and failure stories here. Both long tries and short ones. My goal is to find ways of presenting Scala to another person, friend, co-worker (not an audience) that will make them want to use this great language.

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  • Animate a e.Graphics.DrawLine with arrowhead

    - by Fer
    I need to "animate" an arrow. It can go in any direction (up, down, left, right and diagonals) and the arrowhead will be at the end. It needs to appear as if it is growing from orgin to the end. To make matters more complicated it has to be in a user control so it is possible to add to the controls collection in the forms and remove it to delete it from the screen, and its background is really transparent (no color.transparent) so i can't paint the background to "clear" the previous line. I have it static already (drawn from origin to end) but i can't animate it. I tried to add a timer in the user control but I fail to get a correct algorithm to calculate the intermediate ends of the line while it is growing. Any help would be appreciated. Thanks

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  • How do you use any2mobi command line tool (part of Calibre) to make mobi files from HTML?

    - by Paul Chernoch
    I am on MAC OS X 10.5.5. I installed Calibre, a tool for converting e-book files from one format to another. It has a GUI as well as command line tools. I am trying to run the command line tool "any2mobi" to convert HTML files to MOBI pocket format or Kindle AZW format, with a TOC. I get the error "-bash: any2mobi: command not found". Clearly, any2mobi is not in my path. Where is it? I tried searching but came up empty. I installed version 0.6.0b6 of Calibre.

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  • Is there a way for IIS6 to do http and https together in the same site?

    - by puffpio
    The site needs to be accessible both from HTTP and HTTPS (in case the client wants the form submissions to be secure or not) The site is hosted in IIS6 and ideally I'd like to be able to just have one website in there and it can handle both http and https..is this possible? alternatively i was thinking maybe creating a "secure" subdirectory in the site and duplicating everything in there as well..is that feasible? this is further complicated that it is using asp.net 3.5's routing ability to do url rewrites so even if I create a secure subdirectory, i dunno if it will actually pick up that it's supposed to be SSL approved

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